On some cars manufacturers have gone to a radio antenna with what looks like a spiral wire wrapped around it.
Thule roof bars noise.
All roof bars will make some noise.
The design keeps vortices from slapping back together after the antenna has sliced through them.
The new aero foil cross bars provides a significant improvement in roof rack noise.
They are noisy and when it rains they whistle especially when bike carriers are attached.
You can also wrap some 1 4 to 3 8 rope in a spiral around both bars.
The thule aeroblade and rhino rack vortex bars both feature noise reducing strips that makes them almost silent in many applications.